1. Field of the Invention
The present invention relates to a power semiconductor device, and more particularly, to a power semiconductor device formed using an epitaxial layer on a substrate and a method of manufacturing the power semiconductor layer.
2. Description of the Related Art
Insulated gate bipolar transistors (IGBTS) are favorably considered as power semiconductor devices combining the high-speed switching characteristic of a high-power metal oxide silicon field effect transistor (MOSFET) and the high-power characteristic of a bipolar junction transistor (BJT). A field stop (FS)-IGBT is a kind of the IGBTs. The FS-IGBT can be regarded as a soft punch through IGBT or a shallow punch through IGBT. The FS-IGBT can be understood as a combination of a punch through (PT)-IGBT and a non-punch through (NPT)-IGBT and thus can be considered as having the advantages of the PT-IGBT and the NPT-IGBT, such as low saturation collector voltage (Vce,sat), easy parallel operation, and ruggedness.
Nevertheless, the manufacture of the FS-IGBT requires a thinner flat wafer than the manufacture of the NPT-IGBT, and also requires an n layer between a P collector region and N− drift region so as to prevent the expansion of a depletion region into the P collector region.
There have been proposed various methods for manufacturing the FS-IGBT. However, those methods often exclude epitaxial layers and thus the FS-IBGT is formed in a very thin substrate by a process of implanting and diffusing impurity ions into the very thin wafer.
Since an FS (field stop) layer is formed through the ion implantation or diffusion processes, a high-energy ion implantation process or a wafer thinning process is required before the forming of the FS layer. The process to form the IGBT includes forming the N− drift layer on the FS layer and forming a double diffused MOSFET (DMOS) operation thereon. Those processes are performed on a very-thin wafer and such thin wafers are fragile and are prone to warp or break during ion implantation, annealing and photolithography. Accordingly, there is required a method that makes it possible to use thicker wafers or substrates during the general semiconductor manufacturing processes and to introduce an N-type FS layer between a P collector layer and an N− drift layer that are required in the FS-IGBT structure.